four. continuing efforts to keep the nuclear material cool have failed. early tuesday, explosions ripped through reactor two, possibly damaging the inner steel containment vessel. if it fails, the fuel rods will be exposed, increasing the risk of a partial meltdown. and over at reactor four, which had been shut down since november for maintenance, spent fuel rods caught fire when cooling methods failed there as well. that released high levels of radioactivety into the air. after the fires were extinguished, radiation levels dropped, but officials are concerned the pool walls may be damaged, raising fears of the release of more radiation. for now, reactors five and six, which had also been shut down for maintenance, remain intact. the new fire out there this morning is in reactor four which is a place that has had a series of explosions since last friday.